Self-centering jaw chuck

ABSTRACT

A self-centering, radially reciprocating jaw chuck for machine tools and the like comprising a chuck body member, a plurality of master jaws secured to the body member, each of the master jaws having a pair of circumferentially spaced fixed portions rigidly secured to the body member and a radially reciprocable portion positioned circumferentially between the fixed portions. Resilient means integral with both the fixed portions and the radially reciprocable portion connect these portions, and a work gripping member is secured to each of the radially reciprocating portions. Axially reciprocable means is provided within the body member for radially reciprocating the radially reciprocable portions, and work gripping members attached thereto, whereby flexure of the resilient means provides a self-centering action of the work gripping members with respect to the longitudinal axis of the chuck and the work.

BACKGROUND AND OBJECTS

This invention relates to a radially reciprocating jaw chuck for use onmachine tools such as lathes and the like. More specifically, thisinvention relates to a jaw chuck for machine tools wherein the jaws areself-centering and thereby center the workpiece on the spindle axis.

The prior art is replete with many different constructions forreciprocating jaw chucks, and improvements thereto. One of the morecommon and least expensive constructions is of the type wherein radialstop screws adjust the radial position of the jaws and clamp the jawsonto the workpiece either internally or externally thereof. Each of thescrews is adjusted independently and this type of construction whilegood for holding the workpiece, can result in inaccuracies in centeringthe workpiece on the lathe spindle axis.

Another type of jaw chuck is shown in my U.S. Pat. No. 3,658,353 whichutilizes master jaws to which work gripping jaws are attached. Anaxially slideable cam member engages each of the master jaws resultingin simultaneous actuation of each of the work gripping jaws. In such acase, the draw plug actuator is double acting so as to both open andclose the jaws of the chuck in a positive manner.

Another prior art type of jaw chuck is shown in U.S. Pat. No. 3,685,844which utilizes a hydraulically actuated toggle mechanism for opening thejaws, and uses a built in type resilience in master jaws to close thework holding jaws. This type of arrangement however is typically suitedonly for internal or external gripping, and not both.

All of these prior art types of jaw chucks have advantages anddisadvantages in use, but one disadvantage common to all lies in theability of the chuck to center the workpiece on the center line of thespindle. In the case of a cylindrical workpiece, it is important thatthe axis of the workpiece in the chuck and the axis of the spindle becolinear. Any deviation from colinearity results in whip in theworkpiece with increased wear on the cutting tool and decreased accuracyin the finished product. Additionally, lack of colinearity of the axisof the work and the spindle will result in off-center boring orelliptical turning or other deviations from the desired normal in themachining operation. Accordingly, it is imperative that the workpiece becentered on the spindle axis, and any improvement in the chuck whichwill facilitate the centering greatly reduces the time and skillrequired by the operator. Thus, machining costs can be held down by aself-centering type of jaw chuck.

Accordingly, a primary object of this invention is to provide a jawchuck of the self-centering type.

Another object of this invention is to provide a self-centering jawchuck of durable yet inexpensive construction.

A further object of this invention is to provide a self-centering jawchuck which utilizes independent master jaws.

Still another object of this invention is to provide a jaw chuck ofextremely high accuracy.

Still a further object of this invention is to provide a jaw chuck withrelatively few moving parts.

Still another object of this invention is to provide a self-centeringjaw chuck capable of high accuracy when used by an operator possessinglesser skill.

Yet a further object of this invention is to provide a self-centeringjaw chuck which utilizes a plurality of master jaws having a fixedportion and a radially reciprocable portion resiliently secured theretoand to which work gripping jaws are attached.

These and other objects and advantages of this invention will becomeapparent when considered in light of the following description andclaims taken together with the drawings, in which:

FIG. 1 is a side elevational view in partial section of a chuckaccording to this invention;

FIG. 2 is a right side elevation view of the chuck of FIG. 1;

FIG. 3 is a side elevational view of the master jaws of the chuck ofthis invention;

FIG. 4 is a sectional view along line 4--4 of FIG. 1 and viewed in thedirection of the arrows;

FIG. 5 is a side elevational view of the draw plug actuator of thisinvention;

FIG. 6 is a right side elevational view of the actuator of FIG. 5;

FIG. 7 is a front elevational view of one of the master jaws of thisinvention in its normal state;

FIG. 8 is a view similar to FIG. 7 showing the master jaw in itsexpanded state;

FIG. 9 is a sectional view along line 9--9 of FIG. 7 and viewed in thedirection of the arrows;

FIG. 10 is an exploded view of a portion of the actuator, and

FIG. 11 is a plan view of an alternate embodiment of the master jaws.

DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 of the drawings, the chuck generally designated10 is seen to comprise a body member 12 mounted on a spindle 14. Aplurality of master jaws 16 are attached to the body member 12.

Body member 12 is seen to include an inner flange 18 to which is bolteda guide bushing 20 by means of bolts 22. The inside of the guide bushing20 is provided with a pair of bearings 24. The bearings 24 mount a drawplug 26 therein to permit axial movement of the draw plug. A draw collar28 is positioned around the draw plug 26 and abuts against shoulder 30of draw plug 26 and is secured in place by means of nut 32 which in turnis locked in place by means of set screw 34. Draw collar 28 is providedwith a keyway 36, and key screw 38 engages keyway 36 to prevent relativerotation of the draw collar 28 and the spindle 14. A lock screw 40maintains key screw 38 in position.

A screw 42 is provided in bore 44 to lock the chuck body member 12 tothe spindle 14.

Secured to the front face of the chuck body member 12, are a pluralityof master jaws 16 as seen in FIGS. 1, 3, 4, 7 and 8. Master jaws 16 aresecured to the body member 12 by means of bolts 46 passing into bores 48in the master jaw 16 and body member 12, and into threaded bores 50 inthe body member 12. These screws fit tightly into bores 48 and act asdowels to eliminate any movement between jaws 16 and body member 12.

As best seen in FIG. 1, a cap screw 58 is provided with a shank portion60 and a threaded portion 62. The threaded portion 62 threadedly engagesthe body member 12. A bushing 64 surrounds the shank portion 60 of thescrew 58. Bushings 64 are ground simultaneously with the surfaces of themaster jaws 16 and subsequently, the bushings 64 are removed whilegrinding is continued on the surfaces of the master jaws 16. The resultis that master jaws 16 have a thickness slightly less than the length ofthe bushings 64. This difference is preferably on the order of 0.0005inches. Thus, when the cap screw 58 is tightened, it bears against thebushing 64 and not against the master jaws 16. This provides a slightoperating clearance between the master jaws 16, and the head portion ofthe screw 58.

The master jaws are shown in position on the body member 12 in FIG. 4and FIG. 7 shows one of the jaws in its normal relaxed state. Withreference to FIG. 7, each of the master jaws 16 is formed preferably byinvestment casting of a suitable alloy such as steel which will bespring tempered. Slots 68 and 70 terminate in circular bores 72 and 74which serve to relieve stress at the inner ends of the slots. Slots 76and 78 are preferably substantially perpendicular to slots 68 and 70,and terminate in oval openings 80 and 82 the major axes of which aresubstantially parallel to slots 68 and 70. Webs w are formed in theslots 68, 70, 76 and 78 during the casting process. After the masterjaws are surface ground as discussed supra, the webs w are sawed ormachined out thus opening the slots and permitting the necessaryflexing. FIG. 7 shows one of the webs w before it is cut out.

As previously discussed, the master jaws 16 are secured to the chuckbody member 12 by means of bolts 46 passing through bores 48. By virtueof this means of attachment, and the slot configuration as shown anddescribed, the portions 84 of the master jaws 16 are fixed securely tothe chuck body member 12. The work gripping jaws 66 are bolted to themaster jaws by means of bolts 85 passing through the jaws 66 intothreaded holes 86 and by means of dowel pins 87 passing from the workgripping jaw 66 into bores 88 in the master jaw 16. The slotconfiguration as described permits a flexure and resultant radialreciprocating motion of the radially reciprocable portion 90 of themaster jaws 16, carrying therewith the work gripping jaws 66. This isprovided by means of a pivotal action at points A, B, C, D, E and F atthe termini of the respective leaf-spring-like members 92, 94, 96, and98 which are formed by the cutout portions 68, 70, 80 and 82. Becauseeach of the master jaws 16 is symmetrical with respect to the sectionline 9--9 which is also a radius of the chuck body member, an equalflexure on each of the work gripping jaws 66 is obtained. Thissymmetrical flexure force is the action which provides theself-centering aspect of this chuck construction. Additionally, thesymmetry afforded by this construction eliminates any force imbalance onthe rotating mass which would otherwise be encountered, thus furtherenhancing the accuracy capabilities of this construction.

With reference to FIGS. 7 and 9, each of the master jaws 16 is providedwith cam surfaces 100, 102 and 104. These surfaces cooperate with thedraw plug 26 in a manner hereinafter described to effect actuation andradial reciprocation of the radially reciprocable portion 90 of themaster jaws 16, as well as the attached work gripping jaws 66. The drawplug 26 includes a head portion 106 having the configuration as shown inFIGS. 5 and 6, and is provided with tapered, flat surfaces 108 havingthreaded bores 110. A cam plate 112 rests on the flat surfaces 108, andthe cam plate 112 is provided with a U-shaped cutout 114. A cam head 116rests upon cam plate 114 and has a counterbored hole 118 passingtherethrough. A bolt 120 passes through the hole 118, the U-shapedcutout 114 and threadedly engages the bores 110. A bushing 121 ispositioned around the bolt 120 within the cutout portion 114 so as topermit relative sliding movement of the cam plate 112 with respect tothe surface 108 and cam head 116. The cam plate 112 is bolted tosurfaces 102 and 104 of the master jaws 16 by means of bolts 122 whichthreadedly engage bores 124 in the master jaws 16. Prior to theirinstallation on the chuck during their manufacture, bushings 121 and camplates 112 are surface ground together on a surface grinder to providesmooth surfaces and equal thicknesses of all of these parts. Then thebushings are removed while the grinding of the cam plates continues soas to reduce the thickness of the cam plates to about 0.0005 inches lessthan that of the bushings 121. This provides a slight operatingclearance between cam plate 112 and cam head 116 and permits relativesliding of these parts without binding.

This technique of grinding bushings 121 and cam plates 112, as well asbushing 64 and master jaws 16, to provide slight clearances would atfirst seem to reduce the accuracy of such a chuck since a slight amountof free play is introduced. However the amount of play can be veryprecisely controlled and interchangeability of large numbers of partsassured at extremely low cost when compared with the usual hand fittingof chuck parts. Repeatability in accurately positioning a workpiece istremendously improved with this method with very low manufacturing cost.Tests have shown this to be true by repeatedly positioning a givenworkpiece to within 50 millionths of an inch. Thus this chuck hasextremely high, repeatable accuracy.

To further augment the accuracy capabilities of the chuck, flat surfaces150 are accurately ground on the jaws 66, and a pin 152 is insertedtherein and the chuck then is tightened to grip the pin 152. Next, thejaws 66 are turned while on the lathe to a size to fit the work beingheld. Thus, accurate gripping surfaces on the jaws 66 may be machined.

OPERATION

In operation, when it is desired to move the work gripping jaws 66radially inwardly to grip a workpiece, the draw plug 26 is moved to theleft as seen in FIG. 1, carrying with it the cam head 116. The surface126 of cam head 116 bears against surface 128 of cam plate 112 which isin turn secured to the master jaw 16. Because of the relative slidingmotion of members 112 and 116 along surfaces 128 and 126 respectively,the radially reciprocable portion 90 of master jaws 16 are caused tomove radially inwardly as draw plug 26 is moved to the left as seen inFIG. 1, and moved radially outwardly as the draw plug 26 is moved to theright as seen in FIG. 1. During this radial reciprocation of theportions 90, the fixed portions 84 of the master jaws remainsstationary. The flexure of the leaf spring members, 92, 94, 96 and 98thusly provides a self-centering action of the work gripping jaws 66 onthe workpiece.

In this manner, both a positive gripping and releasing force is obtainedin operation of the chuck, thus securely gripping the workpiece during amachining operation whether the workpiece is gripped internally orexternally. The screw 58 with the bushing 64 provide the necessaryclearance between the head of screw 58 and body member 12 to allowportion 90 of jaws 16 to move freely while preventing its lower portionfrom moving outwardly away from body member 12.

Thus the chuck of this invention provides for highly accurate machiningof workpieces held therein, and the self-centering action of the chuckpermits ready and facile insertion of the workpiece into the chuck onthe spindle centerline.

With reference to FIG. 11 an alternate embodiment of the master jaws isshown. Here, work gripping jaws (not shown) are secured to the masterjaws 130 by means of screws passing into threaded bores 132 and a dowelpin passing into bore 134 and the master jaw 130 is secured to the chuckbody by bolts passing through threaded bores 136 and a dowel pin passingthrough bore 138. In this construction, portion 140 is fixed whileportion 142, carrying the work gripping jaws flexes by means of slots144, 146 and 148 to permit self-centering of the work gripping jawssimilarly to the previously described embodiment.

While this invention has been described, it will be understood that itis capable of further modification, and this application is intended tocover any variations, uses and/or adaptations of the invention followingin general, the principle of the invention and including such departuresfrom the present disclosure as come within known or customary practicein the art to which the invention pertains, and as may be applied to theessential features hereinbefore set forth, as fall within the scope ofthe invention or the limits of the appended claims.

What is claimed is:
 1. A radially reciprocating jaw chuck for machinetools and the like comprising:a. a chuck body member, b. a plurality ofmaster jaws, c. each of said master jaws .Iadd.being symmetrical about aradial line passing through the center thereof and .Iaddend.furtherhaving a .[.pair of circumferentially spaced.]. fixed .[.portions.]..Iadd.portion .Iaddend.rigidly secured to said body member and aradially reciprocable portion .[.positioned circumferentially betweensaid fixed portions.]., d. .Iadd.a pair of leaf members.Iaddend.resilient .[.means.]. integral with and connecting said fixed.[.portions.]. .Iadd.portion .Iaddend.and said radially reciprocableportion .Iadd.and chordally disposed with respect to said bodymember.Iaddend., e. work gripping members secured to each of saidradially reciprocable portions, f. cam means axially reciprocable insaid body member .[.for.]. .Iadd.operable to .Iaddend.radially.[.reciprocating.]. .Iadd.reciprocate .Iaddend.said radiallyreciprocable portions and associated work gripping members between workgripping and release positions, g. whereby the flexure of said resilient.[.means provides.]. .Iadd.leaf members provide .Iaddend.aself-centering action of said work gripping members with respect to thelongitudinal axes of the chuck and the work. .[.
 2. A jaw chuck as inclaim 1 and wherein:a. each of said master jaws is symmetrical about aradial line passing through the center thereof..]. .[.3. A jaw chuck asin claim 2 and wherein: a. said integral resilient means comprises leafmeans..]. .[.4. A jaw chuck as in claim 3 and wherein: a. said leafmeans comprises a pair of leaf members associated with each of saidmaster jaws..].
 5. A jaw chuck as in claim .[.4.]. .Iadd.1 .Iaddend.andwherein:a. each of said leaf members of each pair is substantiallyU-shaped with each leg of each leaf member of each pair being parallelto the other legs of said pair.
 6. A jaw chuck as in claim 5 andwherein:a. said body member is circular, and b. each leg of each leafmember of each pair is chordally disposed with respect to said bodymember.
 7. A jaw chuck as in claim .[.2.]. .Iadd.1 .Iaddend.andwherein:a. said axially reciprocable cam means comprises a draw plugaxially reciprocable in said body member, b. a cam plate member securedto each of said master jaws on an inner surface thereof, c. a recess ineach of said master jaws adjacent said cam plate member, d. an elongateslot in each of said cam plate members, e. a cam head in each of saidrecesses between said cam plate member and said master jaw, f. boltmeans passing through said slot for securing said cam head to said drawplug, g. whereby upon reciprocation of said draw plug, said cam headacts on said cam plate to radially reciprocate said cam plate and saidmaster jaw.
 8. A jaw chuck as in claim 7 and including: a. a bushingaround said bolt means and positioned in said slot.
 9. A jaw chuck as inclaim .[.2.]. .Iadd.1 .Iaddend.and including:a. spacer means having athickness slightly greater than the thickness of said master jaws formaintaining an operating clearance between said work gripping membersand said fixed portions and between said radially reciprocable portionand said body member.
 10. A jaw chuck as in claim 9 and wherein:a. saidspacer means comprises a plurality of bolts positioned in spaces betweensaid master jaws, b. each of said bolts having an enlarged head portion,a shank portion, and a thread portion, c. a bushing member having athickness slightly greater than the thickness of said master jaws andpositioned around said shank portion, d. said thread portion threadedlyengaging said body member, and e. recesses formed in said work grippingmembers to provide working clearance around said head portion.
 11. A jawchuck as in claim 6 and wherein:a. said leaf members, said fixedportions and said radially reciprocable portions are all defined byslots provided in said master jaws.
 12. A jaw chuck as in claim 11 andincluding: a. three of said master jaws.
 13. A master jaw for use in areciprocating jaw chuck comprising:a. an element having a configurationgenerally of a truncated sector, b. said element being symmetrical, c. afirst pair of slots of substantially equal length extending chordallyinwardly from .[.said arc.]. .Iadd.the outer periphery of said truncatedsector.Iaddend. , d. a second pair of slots of substantially equallength extending into said element substantially perpendicularly to saidfirst slots and having terminal portions extending outwardlysubstantially parallel to said first slots, e. said slots dividing saidelement into two spaced portions attachable to a chuck body and anintermediate portion movable with respect to said spaced portions forsupporting a work gripping jaw.
 14. A master jaw as in claim 13 andwherein:a. said truncated sector is formed by two radii, an includedarc, and a chord intersecting said radii.
 15. A master jaw as in claim14 and wherein:a. said element is symmetrical with respect to a radialline bisecting the angle between said two radii.
 16. A master jaw as inclaim 15 and wherein: a. said first pair of slots are substantiallyparallel to said chord.
 17. A master jaw as in claim 16 and wherein:a.said second pair of slots are substantially parallel to said radial lineof symmetry.